Federica Mogherini, the EU foreign policy chief, said after six and a half years of war it was completely unrealistic to believe that the future of Syria would be exactly the same as its past. The EU wanted “a meaningful and inclusive transition in Syria” open to Syrians from all backgrounds, she said. “It is for the Syrians to decide, but for all Syrians.”

The French foreign minister, Jean-Marc Ayrault, was more specific: “France does not believe for an instant that this new Syria can be led by Assad.”

The fine-tuning of the EU stance on Syria comes ahead of a major aid conference in Brussels, which is partly an attempt to boost momentum behind UN-led peace talks.

In a communique, EU foreign ministers meeting in Luxembourg agreed the EU would only get involved in reconstruction of the war-shattered country once a “comprehensive, genuine and inclusive political transition” was firmly under way.

The EU stance contrasts with the US administration, which said last week that getting rid of Assad was no longer a priority. “You pick and choose your battles,” said Nikki Haley, the US ambassador to the UN. “It’s about changing up priorities and our priority is no longer to sit there and focus on getting Assad out.”

Haley accused the Assad regime, as well as Iran and Russia, of committing war crimes and said the US was focused on pressuring the Syrian leader “so that we can start to make a change”.

On Wednesday the EU will co-host an international summit in Brussels to raise money for Syrian refugees, following a similar event in London last year. Delegates from 70 countries are expected to attend the meeting, which is also organised by Germany, the UK, Norway, Kuwait, Qatar and the UN.

But Turkey, host of close to 3 million Syrian refugees, has refused to confirm whether it plans to attend. Mogherini played down suggestions that Ankara’s refusal to reply to the EU invitation to prime minister Binali Yıldırım was a sign of political strains. “I would rule out tension on Syria with Turkey, on which we’re continuing to work well,” she said in response to a question linking the event to recent rows between Ankara and several European capitals.

Staffan de Mistura, the UN mediator, will meet Syrian civil society representatives alongside Mogherini in Brussels on Tuesday. After holding separate talks with the Syrian regime and Syrian opposition groups last week, Mistura said he did not see an imminent peace agreement, although both sides wanted to continue the process.

In a letter to the Guardian, more than 80 parliamentarians have warned the EU against jumpstarting a large-scale reconstruction programme without a consensus-based political settlement. Such an approach “could become an implicit endorsement of Assad’s control over Syria and hence a betrayal to the aspirations of large parts of Syria’s civil society” the cross-party group of parliamentarians write.

“The EU should now leverage its role as the largest financial donor, to demand a say in any negotiations on the political transition and the future of Syria.”

The letter echoes warnings from Syrian NGOs, who fear that premature reconstruction could lend unwitting support to Assad.

“The EU has leverage, there should be a clear and just criteria for funding projects,” said Fadi Hallisso, co-founder of a relief and development group based in Lebanon. The EU “card of reconstruction and funding can be played once and then you lose it”, he said, calling on foreign actors to back a government that would guarantee justice for all Syrians.

Hallisso was speaking at the launch of a Syrian civil society advocacy alliance, We Exist, which seeks to strengthen the voice of NGOs in talks on the country’s future. He said he feared that a push for reconstruction would obscure the plight of Syrian refugees, many of whom are stuck in limbo without education or work. “Improvement on these files is much more important than reconstruction and much more urgent.”

Oussama Jarrousse, who co-founded Citizens for Syria, said talk about reconstruction was a big distraction. “We still have active conflict, we still have clashes every day, we still have airplanes bombing, we have a very fluid situation with Isis controlling part of Syria. There is a huge humanitarian crisis and the economy has been shattered.”

But while reconstruction was “a big distraction” he said efforts were needed to maintain institutions so Syria did not go further down the road of becoming a failed state.